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Bird predation on cutworms (Lepidoptera: Noctuidae) in wheat fields and chlorpyrifos effects on brain cholinesterase activity
Horned larks, Eremophila alpestris (L.), and McCown's longspurs, Calcarius mccownii (Lawrence), were collected at intervals from two winter wheat fields in Montana after aerial application of chlorpyrifos to control cutworms. Both bird species had a high (95–100%) incidence of Lepidoptera, mostly pale western cutworms, Agrotis orthogonia Morrison, in their stomachs at 3 days postspray. Incidence of cutworms and other insects in stomachs of birds from sprayed fields was lower at 9 and 16 days postspray than in control birds, presumably due to insecticide-caused reduction of insects. Effects of birds on population dynamics of insect pests in wheat are unknown, but birds do contribute to cutworm mortality. Predation is one of the limiting factors to cutworm increase and can supplement insecticidal control. Brain cholinesterase activity in horned larks collected from the sprayed fields at 3 and 9 days postspray was significantly lower than in unexposed larks, but at 16 days the difference was not significant. Although nontarget birds clearly were exposed to chlorpyrifos and manifested a sublethal physiological response, toxic effects were lesssevere than those resulting from endrin application for cutworm control in wheat. More study is needed of larger chlorpyrifos-treated fields under a variety of conditions to fully assess effects on nontarget life.
Tamarisk control on public lands in the desert of southern California: two case studies
As a land manager, the Federal Government faces enormous challenges from exotic pest invasions and associated changes to the structure and stability of native ecosystems (Bureau of Land Management, 1988). On public lands administered by the Bureau of Land Management (BLM) alone, it is estimated that almost three million hectares are occupied by invasive exotic plant species (weeds). Assuming an annual rate of invasion of 14 percent, 930 hectares of BLM-administered land are infested everyday by weeds (Jerry Asher, personal communication). When one considers the fact that BLM administers only about one-third of the public land in the United States (The Keystone Center, 1991), the magnitude of the problem assumes staggering proportions. The scenario described in the quote above portrays only some of the problems associated with the spread of the exotic plant tamarisk, a species on the California Exotic Pest Plant Council’s list of exotic pest plants of greatest concern (California Exotic Pest Plant Council, 1993). In this paper we review the threats posed by tamarisk invasion and proliferation and examine the traits that make the plant such a successful competitor. In addition, we highlight two tamarisk control efforts conducted by the Bureau of Land Management in the southern California desert.
Brown treesnake ( Boiga irregularis ) fact sheet for Pacific Island residents and travelers
The brown treesnake is an introduced species on Guam that has become a serious pest. The snakes probably arrived on Guam hidden in ship cargo from the New Guinea area, about 1100 miles to the south. The first sightings were inland from the seaport in the early 1950s. Snakes became conspicuous throughout central Guam by the 1960s, and by 1968, they had probably dispersed throughout the island. In the absence of natural population controls and with vulnerable prey on Guam, the snakes have now become an exceptionally common pest, causing major ecological and economic damage on the island.
Biophysical warming patterns of an open-top chamber and its short-term influence on a Phragmites wetland ecosystem in China
Passive-warming, open-top chambers (OTCs) are widely applied for studying the effects of future climate warming on coastal wetlands. In this study, a set of six OTCs were established at a Phragmites wetland located in the Yellow River Delta of Dongying City, China. With data collected through online transmission and in-situ sensors, the attributes and patterns of realized OTCs warming are demonstrated. The authors also quantified the preliminary influence of experimental chamber warming on plant traits. OTCs produced an elevated average air temperature of 0.8°C (relative to controls) during the growing season (June to October) of 2018, and soil temperatures actually decreased by 0.54°C at a depth of 5 cm and 0.46°C at a depth of 30 cm in the OTCs. Variations in diel patterns of warming depend greatly on the heat sources of incoming radiation in the daytime versus soil heat flux at night. Warming effects were often larger during instantaneous analyses and influenced OTCs air temperatures from −2.5°C to 8.3°C dependent on various meteorological conditions at any given time, ranging from cooling influences from vertical heat exchange and vegetation to radiation-associated warming. Night-time temperature depressions in the OTCs were due to the low turbulence inside OTCs and changes in surface soil-atmosphere heat transfer. Plant shoot density, basal diameter, and biomass of Phragmites decreased by 23.2%, 6.3%, and 34.0%, respectively, under experimental warming versus controls, and plant height increased by 4.3%, reflecting less carbon allocation to stem structures as plants in the OTCs experienced simultaneous wind buffering. While these passive-warming OTCs created the desired warming effects both to the atmosphere and soils, pest damages on the plant leaves and lodging within the OTCs were extensive and serious, creating the need to consider control options for these chambers and the replicated OTCs studies underway in other Chinese Phragmites marshes (Panjin and Yancheng).
Mass control of insects: The effects on fish and wildlife
The mass control of insects carried on during the past ten years has made possible the economical suppression and, in a few instances, the near eradication of pest insect populations over widespread areas. These large operations, usually featuring the use of the airplane for applying insecticides quickly and cheaply, have proven to be the means of effectuating control programs which never could have been carried on through use of the techniques and equipment of early-day economic entomology. With the development of the methods employed in modern mass control came the introduction of new toxicants, well-adapted for use against insects because of their potency, low cost and wide availability. The present-day entomologist is thus armed with the means to carry on a control task of almost any magnitude.
Evaluation of chemical control for nonnative crayfish at a warm-water fish production hatchery
Invasive crayfish are known to displace native crayfish species, alter aquatic habitat and community structure and function, and are serious pests for fish hatcheries. White River Crawfish (WRC; Procambarus acutus) were inadvertently introduced to a warm-water fish hatchery in Missouri, USA, possibly in an incoming fish shipment. We evaluated the use of chemical control for crayfish to ensure incoming and outgoing fish shipments from hatcheries do not contain live crayfish. We conducted acute (≤24 hr) static toxicity tests to determine potency, dose-response, and selectivity of pesticides to WRC, Virile Crayfish (VC; Orconectes virilis), and Fathead Minnow (FHM; Pimephales promelas). Testing identified a formulation of cypermethrin (Cynoff®) as the most potent of five pesticides evaluated for toxicity to crayfish. A 4-hr exposure to a cypermethrin concentration of 100 μg · L-1 was found to kill 100% of juvenile and adult WRC; however, adult VC were not consistently killed. Concentrations of cypermethrin ≤100 μg · L-1 did not cause significant (>10%) mortality in juvenile FHM. Additional testing is needed to examine selectivity between crayfish and hatchery fish species. Biosecurity protocols at hatcheries that use chemical control have the potential to reliably prevent inadvertent transfers of live crayfish in fish shipments.
Anticoagulant rodenticides and wildlife: Concluding remarks
Rodents are known to affect human society globally in various adverse ways, resulting in a widespread demand for their continuous control. Anticoagulant rodenticides (ARs) have been, and currently remain, the cornerstone of rodent control throughout the world. Although alternative control methods exist, they are generally less effective. ARs work by affecting vitamin K metabolism, thereby preventing the activation of blood clotting factors and eventual coagulopathy. Since ARs are non-selective, their undoubted benefits for rodent control have to be balanced against the environmental risks that these compounds pose. Although they have been used for decades, pharmacokinetic and toxicokinetic data are mainly available for laboratory mammals and have concentrated on acute effects. Limited information is available on chronic exposure scenarios and for wildlife species. Important gaps exist in our understanding of the large inter- and intra-species differences in sensitivity to ARs, especially for non-target species, and in our knowledge about the occurrence and importance of sub-lethal effects in wildlife. It is clear that mere presence of AR residues in the body tissues may not indicate the occurrence of effects, although unequivocal assessment of effects under field conditions is difficult. Ante-mortem symptoms, like lethargy, subdued behaviour and unresponsiveness are generally not very specific as is true for more generic post-mortem observations (e.g. pallor of the mucous membranes or occurrence of haemorrhages). It is only by combining ante or post-mortem data with information on exposure that effects in the field may be confirmed. We do know however that a wide variety of non-target species are directly exposed to ARs. Secondary exposure in predators is also widespread although there is limited information on whether this exposure causes actual effects. Exposure is driven by ecological factors and is context specific with respect to spatial habitat configuration and bait placement. Another key factor that affects the interaction between ARs and wildlife is the development of resistance in target species. The development of resistance has resulted in higher use of SGARs, thereby increasing the potential of non-target and secondary exposure. AR use has increasingly become more strictly regulated, increasing the need for alternatives. Alternatives are available, including non-anticoagulant rodenticides, but these may also pose significant risk to environmental organisms, humans and pets. There are also various mitigation measures that can be implemented when using ARs, including bait protection, pulsed baiting at the onset of infestation, restricting use by non-professionals, and avoiding use in areas of high non-target density. Reduction in secondary exposure may result from e.g. non-chemical control, habitat management, and, in agricultural habitats, the use of lure crops and supplemental feeding. Such Integrated Pest Management (IPM) may not only reduce non-target exposure but also benefit resistance management. Barriers to adopt IPM approaches however, include the perception that they do not work or too slowly and are more laborious, expensive and time consuming. It is therefore important that the expectations of stakeholders are considered and managed. Nevertheless, further development of alternatives and IPM measures is essential, so the key research priority related to rodent control may ultimately be to address the lack of scientific assessment of the effectiveness of both specific AR mitigation measures and of IPM approaches to rodent control.
Nonlinearity and seasonal bias in an index of brushtail possum abundance
Introduced brushtail possums ( Trichosurus vulpecula ) are a widespread pest of conservation and agriculture in New Zealand, and considerable effort has been expended controlling populations to low densities. A national protocol for monitoring the abundance of possums, termed trap catch index (TCI), was adopted in 1996. The TCI requires that lines of leghold traps set at 20-m spacing are randomly located in a management area. The traps are set for 3 fine nights and checked daily, and possums are killed and traps reset. The TCI is the mean percentage of trap nights that possums were caught, corrected for sprung traps and nontarget captures, with trap line as the sampling unit. We studied 1 forest and 1 farmland area in the North Island, New Zealand, to address concerns that TCI estimates may not be readily comparable because of seasonal changes in the capture probability of possums. We located blocks of 6 trap lines at each area and randomly trapped 1 line in each block in 3 seasons (summer, winter, and spring) in 2000 and 2001. We developed a model to allow for variation in local population size and nightly capture probability, and fitted the model using the Bayesian analysis software BUGS . Capture probability declined with increasing abundance of possums, generating a nonlinear TCI. Capture probability in farmland was lower during spring relative to winter and summer, and to forest during summer. In the absence of a proven and cost-effective alternative, our results support the continued use of the TCI for monitoring the abundance of possums in New Zealand. Seasonal biases in the TCI should be minimized by conducting repeat sampling in the same season.
The future of biocontrol in the Anthropocene: A review of climate change impacts on biocontrol agents and their hosts
Biological control, the practice of using one species (biocontrol agent) to control the population of another (a host or prey species, hereafter target), can be a successful method to reduce pest species in agricultural and natural systems worldwide. Successful biocontrol agents often share a deep evolutionary history with their targets that results in high target specificity and synchronized phenology. However, with rapidly changing climatic conditions, users of biocontrol agents have questioned how climate change will affect both well-established and more recent biological control relationships. Using a meta-analysis of data collected from a systematic literature review, we evaluated the evidence for the impact of changing temperatures on the efficacy of biocontrol agents and corresponding responses in their targets. Overall, most studies of climate change impacts on biocontrol agents take place in the laboratory and focus on arthropod agents that are parasitoids. Results from our meta-analysis reveal that changes in temperature are projected to impact biocontrol agents and their targets similarly, with no overall significant changes to biocontrol agent or target performance. However, our results also show that temperature responses vary widely across study systems, as illustrated by case studies showing both positive, neutral, and negative effects of temperature on biocontrol agent efficacy, as well as variation in responses across the three core biological control measures of success: survival, reproduction, and efficacy. Our work highlights important knowledge gaps including how climate change will affect both biocontrol agents and their targets simultaneously. Additionally, we find that most current studies of climate impacts examined temperature relationships, predominantly of agricultural biocontrol agents. Increasing the breadth of studies is crucial for understanding the potential for climate change to affect the success of current and future biological control programs.
Toxicity of a management bait for grass carp (Ctenopharyngodon idella) incorporated with Antimycin A
No current technology can specifically target grass carp ( Ctenopharyngodon idella ) for control within aquatic ecosystems. Rotenone and Carbon Dioxide-Carp are currently the only available registered pesticides for grass carp; they are nonselective and typically applied throughout the water, equally exposing target and native species. A more selective control tool or pesticide application could be used by resource managers to support mitigation efforts. Development of delivery systems that exploit carp feeding strategies could increase selectivity of pesticides and minimize effects on native fishes. A pesticide with selective delivery could be less labor intensive and used within an integrative pest management strategy. The present study examined Antimycin A toxicity in juvenile and sub-adult grass carp and rainbow trout ( Oncorhynchus mykiss ) across two routes of exposure. Water-based toxicity studies were used to calculate the concentration to cause lethality in 50% of treated fish (LC 50 ) at 24-h, while oral gavage toxicity studies were used to calculate the dose to cause lethality in 50% of treated grass carp and rainbow trout (LD 50 ) 24- to 96-h. Although rainbow trout were more sensitive than grass carp to Antimycin A through water-based exposure, oral toxicity was similar between species, even with inherent gastrointestinal morphological differences. Successful delivery of a lethal dose of Antimycin A to grass carp was achieved through an oral route of exposure using the rapeseed bait and shows promise for registration as a control tool and eventual use in pest management plans. Although a lethal dose of Antimycin A could be incorporated into a single bait pellet, more bait was required to achieve desired mortality when fed to fish under laboratory conditions.
Hydrologic conditions and simulation of groundwater and surface water in the Great Dismal Swamp of Virginia and North Carolina
The U.S. Geological Survey (USGS), in cooperation with the U.S Fish and Wildlife Service, has investigated the hydrology of the Great Dismal Swamp (Swamp) National Wildlife Refuge (Refuge) in Virginia and North Carolina and developed a three-dimensional numerical model to simulate groundwater and surface-water hydrology. The model was developed with MODFLOW-NWT, a USGS numerical groundwater flow modeling program, in combination with the Surface-Water Routing Process, a software package that simulates dynamic surface-water flows, water control structure management, and groundwater/surface-water interactions. The steady-state model was calibrated to average spring conditions by using automated parameter estimation software (PEST) to reduce simulation errors and assess model parameter sensitivity. The model was then used to simulate wet and dry climatic conditions and a variety of hypothetical scenarios in which water levels in the Swamp were raised and lowered by simulated management of water control structures. Results of the model simulations indicate that, under average spring conditions, precipitation is the primary water input (92%); surface-water (5%) and groundwater (3%) inflows make up the remainder. The primary outflow (or loss) is evapotranspiration (55%), with surface outflows (about 41%) and groundwater outflow (about 4%) making up the remainder. Simulated adjustment of water control structure weir levels demonstrates that groundwater levels are affected by water levels in adjacent ditches and that surface-water and groundwater levels can be controlled through management of water control structures, allowing the Refuge to better manage fire risks and preserve forested-wetland ecosystems in the Refuge. The 13 water control structures proposed in the simulated scenario representing possible future conditions effectively raised simulated water levels in the northeastern corner of the study area, a goal of the Refuge management. Results of this study demonstrate use of MODFLOW with the Surface-Water Routing Process for simulating water management options in peat wetlands and will help Refuge managers to better understand existing hydrologic conditions, assess the hydrologic effects of planned changes to water control structures, and apply the new simulation tool to guide water management on the Refuge.
Modeling the compensatory response of an invasive tree to specialist insect herbivory
The severity of the effects of herbivory on plant fitness can be moderated by the ability of plants to compensate for biomass loss. Compensation is an important component of the ecological fitness in many plants, and has been shown to reduce the effects of pests on agricultural plant yields. It can also reduce the effectiveness of biocontrol through introduced herbivores in controlling weedy invasive plants. This study used a modeling approach to predict the effect of different levels of foliage herbivory by biological control agents introduced to control the invasive tree Melaleuca quinquennervia (melaleuca) in Florida. It is assumed in the model that melaleuca can optimally change its carbon and nitrogen allocation strategies in order to compensate for the effects of herbivory. The model includes reallocation of more resources to production and maintenance of photosynthetic tissues at the expense of roots. This compensation is shown to buffer the severity of the defoliation effect, but the model predicts a limit on the maximum herbivory that melaleuca can tolerate and survive. The model also shows that the level of available limiting nutrient (e.g., soil nitrogen) may play an important role in a melaleuca’s ability to compensate for herbivory. This study has management implications for the best ways to maximize the level of damage using biological control or other means of defoliation.
Toward invasive mussel genetic biocontrol: Approaches, challenges, and perspectives
Invasive freshwater mussels, such as the zebra ( Dreissena polymorpha ), quagga ( Dreissena rostriformis bugensis ), and golden ( Limnoperna fortunei ) mussel have spread outside their native ranges throughout many regions of the North American, South American, and European continents in recent decades, damaging infrastructure and the environment. This review describes ongoing efforts by multiple groups to develop genetic biocontrol methods for invasive mussels. First, we provide an overview of genetic biocontrol strategies that have been applied in other invasive or pest species. Next, we summarize physical and chemical methods that are currently in use for invasive mussel control. We then describe the multidisciplinary approaches our groups are employing to develop genetic biocontrol tools for invasive mussels. Finally, we discuss the challenges and limitations of applying genetic biocontrol tools to invasive mussels. Collectively, we aim to openly share information and combine expertise to develop practical tools to enable the management of invasive freshwater mussels.
USGS science and technology help managers battle invading Asian carp
The U.S. Geological Survey (USGS) conducts Asian carp research focused on early detection, risk assessment, and development of control tools and strategies. The goals are to prevent the establishment of invasive Asian carp in the Great Lakes and to reduce their impacts in the Ohio River and Mississippi River Basins and elsewhere. Managers can use the information, tools, and strategies for early detection of Asian carp and to control them when their presence is first evident. New detection and control tools are designed to accommodate expansion to other invasive species and application in geographically diverse areas. This USGS focus complements goals of the Great Lakes Restoration Initiative (GLRI), a multi-agency collaboration started in 2010 to protect and restore the Great Lakes. As a member of the Asian Carp Regional Coordinating Committee, which guides Asian carp efforts, the USGS works closely with Federal and State agencies, Canada, and others to address high-priority Asian carp issues and provide science to inform management decisions. The USGS has gained extensive knowledge of Asian carp biology and life history over the past 30 years. That knowledge guides the design, development, and application of control strategies, and is essential for developing approaches in line with modern principles and practices of integrated pest management (IPM). IPM is a process used to solve pest problems while minimizing risks to people and the environment.
Use of physical blockers to control invasive red swamp crayfish in burrows
The red swamp crayfish Procambarus clarkii is native to the southeast United States but has successfully invaded nearly every continent around the world. Although physical, biological, and chemical controls are employed to reduce or eliminate populations in open-water systems, terrestrial burrows provide a potential refuge from aquatic control treatments. We conducted burrow trials to test whether two physical blocker treatments would kill P. clarkii in their burrows. Bentonite clay (a sealing agent) and expanding foam (an insulating sealant) were each applied to 37 crayfish burrows, and 36 burrows served as treatment controls (i.e., 110 total burrows). Burrows were excavated 48 hr after the application of the physical blockers to assess the status of crayfish in treated and control burrows. There was 74% mortality of crayfish in occupied burrows treated with bentonite clay, 62% in burrows treated with expanding foam, and 6% mortality in control burrows. We believe bentonite clay should continue to be field-tested; however, because expanding foam is toxic to aquatic organisms and is expected to persist in the environment, we do not believe it is a suitable physical blocker for the control of invasive crayfish in burrows. Bentonite clay applications likely will not need permits, will mitigate damage to banks and levees caused by burrowing crayfish, and can be used with other control agents such as pesticides. However, the use of physical blockers may be limited at field sites that have burrows with complex morphologies. We believe the use of bentonite clay to control invasive crayfish in terrestrial burrows will provide resource managers with an effective tool for their integrative pest management programs.
The dilemma of pest suppression in the conservation of endangered species
In the conservation of endangered species, active suppression of a population of one native species to benefit another native species poses particular challenges. Obvious examples include predator control and nest parasite reduction. Less obvious is the control of blood-feeding arthropods. We present a case study on the effect of blood-feeding black flies (Simulium spp.) on reintroduced Whooping Cranes (Grus americana). Our intent is to provide a transferrable, science-driven approach for determining the effects of blood-feeding arthropods on endangered vertebrates, and demonstrate an approach for guiding selection of management actions for managers faced with competing objectives. A multi-year experiment demonstrated that black flies reduce nest success in reintroduced cranes by driving the birds off their nests during incubation. Deciding how to respond, however, is complicated because the target black flies are native species that serve important ecological functions. We suggest that a decision-analytic approach can inspire the development of creative management alternatives and facilitate a transparent process that evaluates trade-offs among competing objectives. Recognizing that these decisions involve trade-offs, which must be weighed in the context of each case, is crucial to identifying alternatives that best balance multiple management objectives. Given the uncertainty about the population dynamics of blood-feeding arthropods, an adaptive management approach will offer substantial benefits.
Invasive species control and management: The sea lamprey story
Control of invasive species is a critical component of conservation biology given the catastrophic damage that they can cause to the ecosystems they invade. This is particularly evident with sea lamprey ( Petromyzon marinus ) in the Laurentian Great Lakes. Native to the Atlantic Ocean, the sea lamprey's ability to osmoregulate in fresh water, its wide thermal tolerance, generalist diet, and high fecundity allowed it to rapidly reach pest proportions in the prey-rich Great Lakes once it gained access through shipping canals. The invasion exacerbated declines in Great Lakes fisheries caused by overharvest, culminating in the crash of lake trout ( Salvelinus namaycush ) and other fish populations. In the last 60 years, however, a highly successful sea lamprey control program has reduced sea lamprey to ∼10% of their peak abundance and has been instrumental in enabling the rehabilitation of the Great Lakes ecosystem. In this chapter, we: (1) discuss the likely vectors of the invasion and the physiological attributes of sea lamprey that enabled them to become established in the Great Lakes; (2) review the two cornerstones of the sea lamprey control program—which relies on a combination of pesticides to eradicate multiple generations of larval sea lamprey in their nursey streams, and in-stream barriers to restrict the upstream migration of spawning lamprey—both of which exploit unique physiological vulnerabilities of sea lamprey; (3) describe how sea lamprey control can adversely affect non-target species and how these can be mitigated; (4) show how physiology-based approaches are improving our understanding of the lethal and sublethal effects of sea lamprey on host fishes; and (5) discuss the future of conservation physiology in sea lamprey control. The prime challenge in the next several decades of the Anthropocene will be to further refine the specificity of control tools while maintaining their efficacy, and to adapt to a warming climate and other anthropogenic activities affecting the Great Lakes and their tributaries.